TOPICS
Real
Story
Conference
on Surface Friction
Recent
TRL Reports
Motto
of the Month
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Introduction
As you may have noticed, those of you who read this newsletter, I gave
myself June and July off.
Well, it is the summer and who wants to be in front of a computer
during the long pleasant evenings when you can be outside mowing the
lawns, trimming shrubs and hacking bits off trees. They all seem to grow at an extraordinary rate at
this time of the year, I blame global warning and the extra carbon
dioxide in the atmosphere the "green things" love it.
I am back after my rest to produce a few more jottings that may be of interest to
some of you.
It is a fact that this page is not widely read, but I am
led to believe some browsers find the content interesting and thought
provoking, others find the content less welcome.
If you have not read my Homepage, may I point out that I do have a day
job, I am a public servant, working for an "organisation"
that is responsible for maintaining a considerable local highway
network.
I am proud of being a public servant and part of a multi disciplined
team that has been acknowledged as being pretty good at what we do.
I see my role as that of providing information that will
allow my colleagues to spend their budgets effectively to maintain a
road network in a safe and durable condition, whilst considering sustainability,
and environmental impact.
It is a delicate balance, with budgets hardly ever sufficient and
often changeable at short notice, making true forward planning
difficult.
In producing this website I am sharing what information I can with a
wider audience, because I feel "old-timer" experience and
knowledge is being lost fast, especially soils and materials knowledge.
There are other people in the industry who have different
responsibilities to those that I carry, they play their part, and
people such as myself play our part, we need the balance.
Real Story - The Killer Beneath Our Wheels
This much awaited documentary, came and went, after being delayed for
two weeks, and the industry has survived, everything seems to be
continuing much as before.
My personal opinion is that as a programme for the general public, it was as good as it could be, and it did raise a number of
issues that are pertinent to providing safe and durable road networks.
With regard to Thin Surfacings, I believe the term was mentioned once
or twice but I believe Fiona "got away with it", without
causing offence.
It was SMA that bore the brunt of the comment, and although I recall
the expression "some SMA's" give cause for concern, are
slippery in the dry, or whatever. I felt the tone of the programme did
suggest that all SMA's have reduced skid resistance compared to other
road surfaces,
which clearly is not the case.
This is particularly disturbing for me because the organisation I work
for has many miles of SMA surfacing, laid over a number of years, and
I am not aware of any accidents on the surfaces we specified being
attributable to problems with early life skid resistance.
(Some of them are showing signs of distress sooner than anticipated
and they are requiring surface dressing earlier than expected, to
prolong the integrity of the surface course layer, but that is a story
for another time.)
I have said this repeatedly, but I will say it again Stone Mastic
Asphalt (SMA) is not one material, Hot Rolled Asphalt (HRA) is not one
material, Bitumen Macadam, dense or open, (CGM / OGM) is not one
material, they are numerous materials, I will not go on, read the April Newsletter.
But I do believe there have been problems with some SMA's due
to the nature of the mixture and the way they have been designed and
produced, and where they have been used.
I further believe the way SMA's have been marketed has contributed to
the situation, suggesting that SMA (and anything called SMA) is some sort of "super
material" that is the cure all for all road surfacing
problems.
It is not, it is a type of material, that needs all the consideration
in design, production and use, just as any road surfacing material
does. Perhaps more so when you consider the substantial mastic layer
that will be presented as the road surface that the vehicle wheel will
come into contact with for a period of time, dependent upon the
level of trafficking.
In saying what I have said I find myself agreeing in part with an
editorial in a recently published journal. The editorial went on to
point out that a "bright, knowledgeable and articulate" (I would like to make a joke here questioning
whether this person really is a member of the highways maintenance
fraternity but it would probably be misconstrued) spokesman for the Asphalt Industry Alliance (AIA) had
been put forward to explain that "there is no evidence that SMA
is any less skid resistant than hot rolled asphalt or any other
asphalt surface".
So, I thought the comments of this spokesman would be contained in the
pages of the journal, so we could all read what he was going to say, I
could not find them, nor could I find a response on the AIA
website.
In fact the usual silence has settled on the industry when its
competency is being challenged.
It will all go
away if we do not talk about it, certainly the lack of
comment/discussion/debate in the main stream engineering journals I
find disappointing.
Are there any truly independent engineering journals
left, perhaps not, but you still get the occasional good paper.
May I recommend, if you have not already read it, "Investigating
high specification aggregates", in the May (possibly June)
edition of the journal Transportation Professional, written by an
engineer of considerable standing in the industry.
A note explains that, "The paper has been prepared and peer
reviewed on behalf of the IHT (Institute of Highways and
Transportation) Asset Management & Sustainable Construction
Panel."
I believe it is a paper you will benefit from reading, and being
involved in the debate it encourages.
But if you cannot find a copy, or you are too busy, the paper suggests
that, " Practitioners with professional responsibility for road
safety and surfacing materials should read the new Capita Symonds
report", (The
Sustainable Use of High Specification Aggregates for Skid-Resistant
Road Surfacing in England).
International
Conference on Surface Friction
In May of this year Transit New Zealand and WDM (UK) hosted an inaugural
international conference on Surface Friction for Roads and Runways in
Christchurch, New Zealand.
Senior researchers, in this field, from all over the world came together
and presented papers relating to their work.
It is extremely pleasing to report that all the papers presented are
available for downloading on the website,
www.surfacefriction.org.nz/
This is an extremely beneficial resource for those seeking guidance on
this topic, there are several papers given by speakers from the UK that
are relevant to the current Thin Surfacing/SMA early life friction
debate in the UK.
Alternately you could "Google" it by using the key words
"sma early life skid resistance" and the appropriate papers
will be presented in the first couple of pages.
Perhaps you would like to start by reading the paper, "An
Investigation of the Skid Resistance of Stone Mastic Asphalt laid on a
Rural English County Road Network", prepared by a group of
engineers from Dorset County Council.
Recent
TRL Reports
I would like to bring to your attention three recently
published reports from TRL (Transport Research Laboratory).
These are all important reports, with perhaps TRL638 being less
"hands-on", and more for the new breed of procurement, and
performance professionals, "bless 'em", but it should not be
ignored by practicing road pavement engineers because it will affect you
sooner or later.
TRL636, and TRL639 have excellent content and in my opinion need to be
studied in depth, not just the executive summary and conclusion.
In giving much good information on how work has been performed to
achieve good results TRL636 worries me a little by then appearing to suggest that
options are being explored to produce materials that are different to
those that have been trialed, (undercover in test facilities with a huge
amount of supervision).
I think people should recall the chequered history that the introduction
of stiff roadbases/bases
into the UK has had to date before they start changing from the
bituminous mixtures that appear successful in the described trials.
Personally, I think it would have been appropriate to have included a
Hot Rolled Asphalt binder course/base mixture as part of the trial,
perhaps with a stiffer binder than 50pen, this being a bituminous
mixture closer in nature/characteristics to an EME than a coated
macadam.
TRL639 has very informative content on the subject of "long life
pavements" and how existing pavements can be upgraded to reach a
"long life" state.
Not planing off areas of good surfacing, where levels permit, and simply
overlaying with a durable thick (40/50mm.) layer after repairing weak
areas would seem an obvious starting point, and one much employed by
"cash strapped" local authorities, well, at least one I know
of.
Read the reports, carefully, and make up your own minds, please do not
sit on the side, and if/when it perhaps goes wrong say it was nothing to
do with you, it was, because you did not play a part.
The reports are :-
TRL Report TRL636 - The application of Enrobé à Module Élevé in
flexible pavements
TRL Report TRL638 - A model set of asphalt sustainability indicators
TRL Report TRL639 - Guidance on the development, assessment and
maintenance of long-life flexible pavements
These reports are obtainable from TRL, I recommend you obtain copies and
study them, there is some very informative content on the existing
procedures for flexible road pavement construction with bituminous
mixtures, and a few interesting new
concepts, such as, just repairing failing wheel tracks and not the whole
carriageway.
See, you're curious already.
Motto of the Month
I am sure this quotation has more profound origins, but this version I
attribute to my "old" mum although she did not live to be
old, but long enough to raise me.
"If all your friends jump in the canal,
I do not expect you to."
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